Japanese patent publication Hei-2-213105 describes a process for monitoring a tap changer whereby different measured values, like pressure, the load on the actuating elements, the current, or impurities in the oil, are detected. The present state of the tap changer is described in terms of these measurements to provide an indication of the actual status of the tap changer, these measured values are stored and the measured values are compared with previously stored, apparatus-specific setpoint values and the comparison used, for example, to shut down the tap changer in the case of an emergency situation or the like. If there are deviations as a result of this comparison, signals are generated which can provide warnings for the automatic shutdown of the tap changer.
German patent document DE 42 14 431 C2 describes a process in which the position of the tap changer is determined and this system can use a position changer which signals the instantaneous position of the drive shaft of a motor drive connected with the tap changer. The output from this generator can be converted into a binary value representing the position of the motor shaft and hardware decoding or a microprocessor controller can be provided to process the binary values which result. In this case the microprocessor controller monitors the position signaled by the position generator of the drive shaft and hence the movement thereof.
Published Japanese application Sho-60-176213 describes a system in which the torque on the drive shaft which is produced by the motor drive and with which the tap changer operates is detected for each actuation of the tap changer, the curve of the torque with time is compared with a setpoint torque curve which may be typical specifically to the tap changer and the result of this comparison is used, if necessary, to shut down the system should need arise. A similar process has also been described in East German patent document 246 409 in which the curve of the torque as a function of time is measured during a tap change operation and the result is compared with a torque curve typical of the tap changer.
As a rule, measured values which are to be compared later with setpoint values are stored as ASCII data. It is possible to effect a data compression to minimize the steps required in the storage medium for storage of the data. The measured values are customarily a succession of absolute values at certain points in time which are applied to the storage medium. The significance of the values depend upon the particular input channels on which the data arrive.
The publication "Hydro TEC HT2000" of Deltatronic Instruments GmbH, of Austria, relates to a process where the information is processed as ASCII data in storage in the following manner, given for a storage space corresponding to 30 bytes.
Starting time with the measured value will be 11:49:11 28 Close of the measurement 12:59:11 17 (17 is the new value for the subsequent measurement.)
__________________________________________________________________________ Address 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F Value FF 31 31 3A 34 39 3A 31 31 20 20 20 32 38 0D 0A Address 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F Value 31 32 3A 35 39 3A 31 31 20 20 20 31 37 0D 0A FF __________________________________________________________________________
A further variant for the storage of measured data is known from the Viereck dissertation: Use of Sensors in Transformers, TU Dresden, Germany 1992. In a fixed time period, which is subdivided into defined time intervals, with a constant analog value, can be broken down in the time intervals into hexidecimal values so that only two addresses of the storage medium need indicate variable time periods.